/Engine/Source/Runtime/GeometryCore/Public/Spatial/BlockedDenseGrid3.h
Note on the block size: 8 seems to be the sweet spot with vastly better performance in SDF generation perhaps because a float block can fit in the L1 cache with room to spare.
typedef [TBlockedGrid3](API\Runtime\GeometryCore\Spatial\TBlockedGrid3)< float, 8 > FBlockedGrid3f